The invention relates to a drilling fluid and, more particularly, to a stable and environmentally safe foamable drilling fluid.
In the course of drilling a subterranean well, drilling fluids are needed in order to lubricate the drill bit and to carry formation cuttings to the surface. In addition, the drilling fluid is needed in order to balance high-pressures encountered in subterranean formation.
Foamed drilling fluids are known and used in situations wherein reduced density is desired, for example in low-pressure formations, wherein the other functions of a drilling fluid are still needed. In low-pressure formations, the use of fluids having higher density can result in a partial or total fluid loss into the formation, which can result in increased drilling cost, formation fracturing and/or damage, and even well loss.
In such instances, under-balanced drilling is typically performed in order to avoid such desirable occurrences and, if necessary, permit a short influx from the formation.
A number of problems are experienced with known foamable drilling fluids. These include short stability periods in the presence of formation contaminants, poor transportation capability, short reutilization cycles and environmental issues.
It is clear that the need remains for a foamable drilling fluid, which is stable in the presence of formation contaminants such as crude oil and/or salt, which has effective cutting transport capability, which exhibits good reutilization cycles through re-generation of foam at the surface, and which is environmentally friendly.
It is therefore the primary object of the present invention to provide a foamable drilling fluid having these properties.
Other objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages have been readily attained.
According to the invention, a foamable drilling fluid is provided which comprises an aqueous solvent, a surfactant, and a guar polysaccharide preferably derived from a galactomannan gum, and most preferably guar gum.
In accordance with a further aspect of the present invention, a foamed drilling fluid is provided, which comprises a liquid phase comprising an aqueous solvent, a polysaccharide preferably derived from a galactomannan gum and a surfactant; and a gas phase selected from the group consisting of nitrogen, air, natural gas, CO2 and combinations thereof.
The polysaccharide additive of the present invention has been found to advantageously provide for excellent stability and cutting transport capacity, while nevertheless being environmentally friendly.